1. Field of the Invention
The present invention relates to vortex blowers, and more particularly, to a vortex blower which eliminates deposition of dust to an inner wall surface of an outer peripheral wall in a vicinity of end portions of blades to thereby reduce the vibration of an impeller due to mass unbalance.
2. Description of the Prior Art
Generally, an impeller of a blower is rotated at an extremely high speed. Therefore, if there is any mass unbalance, the impeller will be vibrated to cause various problems such as, for example damage to mechanical rotor shaft or the impeller, overheating or seizure in the bearings, excessively loud noise and so forth, resulting in a deterioration of the durability of the blower. The vibration also produces noises which seriously deteriorates the working condition or environment.
An example of vortex blowers is disclosed in U.S. Pat. No. 3,355,095. This vortex blower has an annular recess, formed in an impeller and laterally opening around an axis of rotation, a casing arranged to cover the impeller, a suction port and a discharge port formed in the casing, an arcuate recess formed in a portion of the casing which extends between the suction port and the discharge port and opposes to the annular recess, and a plurality of blades mounted in the annular recess. In the operation of the vortex blower of the type described, the air trapped between adjacent blades in the annular recess is displaced from the radially inner portion of the impeller to the radially outer portion thereof by the centrifugal force produced by rotation of the impeller. The flow of air is progressively accelerated as it approaches the radially outer portion of the impeller and is oriented or deflected to flow into the radially outermost portion of the arcuate recess along the inner wall surface of the impeller. In addition, the air which has been introduced into the radially outermost portion of the arcuate recess flows along the inner wall surface of the arcuate recess and is directed to flow from the radially innermost portion of the arcuate recess again into the radially inner portion of the arcuate recess. This movement of the air is continued until the air is discharged from the blower, and thus the air in the casing is repeatedly accelerated by the impeller repeatedly, so that it is possible to attain a high discharge pressure.
In this type of vortex blower, a dust separation or filtration device is disposed at the suction port of the vortex blower, particularly when the blower is used in the air suspending dust. It is, however, extremely difficult to completely remove the dust even with the aid of such a separation or filtration device, and the vortex blower is more or less still subjected to such dust. As the air suspending dust is sucked by the vortex blower, the dust particles are separated by the centrifugal force when the radial flow of air is forcibly changed into axial flow at the radially outermost portion of the impeller, and the dust particles thus separated are deposited on the inner wall surface of the radially outermost portion of the impeller.
Once the deposition of dust takes place, it grows to form a thick layer of dust on the inner wall surface of the radially outer portion of the annular recess. Then, the thick layer of dust is partially separated and drop during rotation of the impeller to produce a mass-unbalance of the impeller which, in turn, causes a heavy vibration of the impeller. Furthermore, the aerodynamic performance of the blower is seriously damaged due to a reduction in the area of air passage attributable to the deposition of dust. In order to remove the dust deposited on the impeller, it has been necessary to disassemble and clean the blower.
Another type of vortex blower is disclosed, for example, in the specification of U.S. Pat. No. 4,247,246 and Japanese Laid-Open No. 120207/1974. In this vortex blower, the deposition of dust is effectively avoided due to the construction which permits air to be discharged radially outwardly from the impeller or in a direction in which centrifugal force acts on dust. This vortex blower, however, requires a sufficient space for surrounding the impeller at the radially outer side and lateral side thereof for changing the flow direction of air. It is, therefore, not possible to preserve a large volume of the annular space in the impeller as compared with the arcuate recess of the casing. According to this arrangement, therefore, it is difficult to attain higher performance of the blower, because the blade area is inevitably smaller as compared with that in the vortex blower of the first-mentioned type.
On the other hand, Japanese Patent Publication No. 33856/1971 discloses another type of vortex blower in which a large area is preserved for the impeller blades with respect to the arcuate recess while effectively preventing the attaching of dust. In this vortex blower, a plurality of semi-circular blades, radially projecting from the impeller are disposed in an annular air passage having a circular cross-section. This vortex blower exhibits a performance equivalent to that achieved by the vortex blower explained above free from the problem of deposition of the dust. In this vortex blower, however, it is necessary to attach the impeller blades at a high precision and to maintain sufficient strength of attaching of the blades, because the impeller faces the inner surface of the casing with an extremely small gap. Namely, in order to avoid mechanical interference between the stationary part and the impeller which rotates at an extremely high speed, it is essential to finish the blade at a high precision. Also, a reinforcement member may be attached to each blade in order to withstand a large stress generated during the rotation of the impeller. This reinforcement member often disturbs the flow of air in the casing.